As is known, refrigeration compartments of any type require an internal lighting device, which is deactivated when the refrigeration compartment is closed; and control and detecting means for controlling and detecting operating parameters of the refrigeration compartment—typically temperature and, possibly, humidity—and comprising at least one electromechanical or electronic thermostat.
Such devices are currently mounted together on a common member defined by a lighting fixture fitted to an interior wall of the refrigeration compartment and comprising a bulb-holder made of synthetic, electrically-nonconducting material and fitted with a light source defined by an incandescent bulb; electronic control means for controlling the light source; and at least one, preferably electronic, thermostat. The bulb-holder also has a transparent cover to protect the bulb.
Known lighting fixtures of the type described above have numerous drawbacks, mostly due to the light source being defined by an incandescent bulb and so constituting an electric element operating at fairly high voltage (typically 220 V mains voltage) and generating a fairly large amount of heat and relatively high operating temperatures.
This therefore calls for precise control of electrical power supply to the incandescent bulb by means of an electronic circuit comprising fairly high-cost components, such as a TRIAC, and a positive-temperature coefficient element (PTC pill) for ensuring the light source is turned off after a given length of time (e.g. in the event the refrigeration compartment door is not closed properly, thus failing to activate the off switch, or in the event of malfunction of the off switch).
Moreover, featuring a mains-voltage-powered element, the lighting fixture must be made according to rigid regulations governing the minimum distance between the high-voltage and low-voltage, typically electronic, components, thus complicating manufacture and increasing bulk.
Moreover, because most refrigeration compartments are cooled by expansion of a refrigeration fluid, which, in most cases, is potentially explosive, known lighting devices must be specially designed to prevent any situation, including accidental breakage of the light source, from generating sparks or at any rate discharging voltage.
Finally, incandescent bulbs have fairly poor lighting characteristics, e.g. they emit a white light with a strong yellowish component, and have a fairly short working life, thus requiring frequent replacement and so posing serious manufacturing problems.
On the other hand, replacing incandescent bulbs with other light sources, such as light-emitting diodes, has always been ruled out by technicians, mainly on the grounds of the high cost (and insufficient lighting power) of such diodes. That is, forming part of electric household appliances such as refrigerators and/or freezers, which have a very small profit margin, the lighting fixtures of refrigeration compartments must necessarily be fairly cheap to produce.